In graphic arts technology, a number of well-established printing processes utilize image carriers with three-dimensional (3D) representation of data the most popular of them being flexographic printing, which uses flexible relief plates or sleeves. In a traditional flexographic prepress process with chemical etching there is no possibility of fine control of relief properties other than depth of relief. A flexographic prepress process, however, use direct laser engraving in place of chemical processes, which permits more detailed control. This enables a 3-D cross-section profile of relief elements to be used as controllable and regulated parameters that bear a direct relation to the quality of resulting image reproduction.
Specifically, the shape of cross-section profile directly influences quality of reproduction of small features such as highlight elements and/or file linework details, process tolerance to changes in pressure applied by plate and/or sleeve to substrate and other vital characteristics. A uniform 3D cross-section profile when applied uniformly on all image elements and features, however, results in sub-optimal performance. The reason for the sub-optimal performance is due to different behavior of the various image elements, such as halftone dots and/or linework elements which may differ in size. Several approaches were proposed to cope with this problem.
One approach is applying a cross-section profile of an imaged printing plate 500 including support layer 520 as shown in FIG. 5. Printing plate 500 shows imaged data elements of different sizes such as 512 and 504. A linear slope cross-section to image elements is applied showing that slope angle is a function of image element size. A shallow angle slope 508 is applied on small printing area 504, whereas a steep angle slope 516 is applied on large printing area 512.
FIG. 6 shows another solution utilizing uniform, but more complex, 3D cross-section profile 600. Profile 600 shows a printing area 604, or a first engraved area situated on base 612 which is wider than printing area 604, forming a two stage shoulders 616 resulting in a total relief size 608. Another solution may be a combination of both of the above solutions.
While producing some improvement, all of the above approaches fail to decisively solve the problem because picture element size as a sole parameter is a suboptimal parameter for cross-section profile shape control. In fact, practical experience shows that local environment of specific feature and local gradient of ensuing relief pattern are more relevant parameters.